This invention relates to a method and apparatus for detecting or judging an end point of polarization titration during analysis of a solution.
When analyzing a solution by polarization titration it is essential to accurately detect the end point of titration. In this specification, a term "titration" is used to include both a method of so-called volume titration in which a titration reagent is introduced into a solution to be titrated and a so-called coulometric titration method in which a titration reagent is formed in a solution to be titrated by electrolysis. Although many methods of judging the end point of titration have been known, according to one method, a pair of platinum detection electrodes are immersed in a solution to be titrated, and a small current is passed between the detection electrodes from a source of constant current so as to judge the end point from the magnitude of polarization potential generated across the electrodes. This method utilizes a phenomenon that the polarization potential varies greatly near the end point of titration, and is used widely as a method of detecting the end point at the time of measuring water content according to Karl Fisher titration process. Among other methods of detecting the end point of titration are included iodometric titration and other oxidation-reduction titrations, and a method of measuring iodine and bromine numbers of fats and oils.
Direct current or alternating current is used for generating polarization between the detection electrodes, but with DC, although the variation in the polarization potential near the end point is large, the polarization potential tends to vary due to the influence of stirring of the solution which makes it difficult to accurately judge the end point. Although the method of using alternating current is not affected by stirring, it accompanies a problem that the variation in the polarization potential near the end point is small which also makes it difficult to accurately detect the end point. These problems can be eliminated to some extent as disclosed in Japanese Pat. No. 933,388.